(A) Field of the Invention
The present invention relates to a method for preparing a structure with high aspect ratio, and more particularly, to a method for preparing a structure with high aspect ratio using a multi-stage etching process incorporating two masks.
(B) Description of the Related Art
FIG. 1 to FIG. 3 are schematic diagrams showing a method for preparing a conductor 22 on a wafer 10 according to the prior art. The wafer 10 comprises a substrate 12, a conductive layer 14 and a dielectric layer 16. At first, a photoresist pattern 18 is formed on the dielectric layer 16 and an etching process is then performed to form a mask pattern 20, wherein the etching process not only removes the dielectric layer 16, but also removes the photoresist pattern 18 completely, as shown in FIG. 2.
Referring to FIG. 3, another etching process is performed to remove a portion of the conductive layer 14 uncovered by the mask pattern 20 to form a conductor 22. The etching process removes not only the conductive layer 14 uncovered by the mask pattern 20, but also removes a portion of the mask pattern 20. In other words, the mask pattern 20 cannot prevent the conductive layer 14 from being removed partially, which will result in an arc profile at the corner of the conductor 22 rather than an expected rectangle profile (shown with dashed line). Consequently, the cross-sectional area of the conductor 22 will reduce, causing the resistance to increase, which is adverse to the conduction of electricity.
In addition, to form a structure with high aspect ratio by increasing the reaction time of the etching process, the mask pattern 20 will be removed completely during the etching process and the conductive layer 14 below the mask pattern 20 will not be prevented from etching. That is, the prior art method does not have the ability to etch downward further to form a structure with high aspect ratio. Consequently, the prior art method is only applicable to preparing the conductor 22 with a lower height, i.e., a structure with smaller aspect ratio, and cannot be used to prepare a structure with high aspect ratio.